Emergy evaluation of reforestation alternatives in Puerto Rico

Six alternative ways of reforesting degraded lands in Puerto Rico were eval uated using emergy (spelled with an "m"). Emergy and its economic equivalen t, emdollars, put the contributions of environmental work and human service s on a comparable basis. This article shows the emergy method for evaluatin g forest contributions to public benefit and its use to select alternatives for reforestation. Emdollar values were compared for six scenarios for ref orestation of degraded land in Puerto Rico: (1) the natural succession with in or adjacent to mature forest; (2) reforestation from the spread of the e xotic tree siris (Albizia lebbek); (3) reforestation with plantations of si ris and mahogany for harvest; (4) reforestation by leaving plantations unha rvested; (5) direct planting of seedlings of many species; and (6) starting patches of forest by massive transfer of topsoil, seed bank, and roots. Af ter energy systems diagrams were made for each reforestation alternative, d ata were assembled and evaluation tables prepared that estimated the emergy required for: (1) canopy closure and (2) developing species complexity if left unharvested. To explain the method, detailed calculations were include d for one of the alternatives, exotic Albizia lebbek plantation on 11 yr ha rvest cycle. All alternatives generated net public benefit (emdollar yield ratios 4.2 to 24.3). The emdollar value of a closed canopy developed in :10 to 20 yr ran ged from 20,000 to 48,000 em$ /ha, whereas the economic costs were $1200 to $9700. For complex forest development in 25 to 60 yr, values ranged from 6 3,000 to 118,000 em$ /ha, much higher than economic costs of $4000 to $12,0 00/ha. Highest public benefit per dollar cost came from succession (24.7 em $/$) and exotic colonization (19.1 em$/$). Highest potential monetary retur ns were from exotic spread (15.1 $/$) and plantations (17.9 and 14.5 $/$). Stand quality after 60 yr, as measured by the transformity (emergy/energy), was largest in mahogany plantation (6.4 x 10(4) sej/J) and succession fore st (3.9 x 10(4) sej/J).